patch 8.1.1076: file for Insert mode is much too big

Problem:    File for Insert mode is much too big.
Solution:   Split off the code for Insert completion. (Yegappan Lakshmanan,
            closes #4044)
diff --git a/src/Make_morph.mak b/src/Make_morph.mak
index af231fb..b224c67 100644
--- a/src/Make_morph.mak
+++ b/src/Make_morph.mak
@@ -49,6 +49,7 @@
 	hardcopy.c						\
 	hashtab.c						\
 	indent.c						\
+	insexpand.c						\
 	json.c							\
 	list.c							\
 	main.c							\